1. Field of the Invention
The invention falls generally in the field of mounting means for wiring devices. In a more particular sense, the invention may be considered as falling into that class of mounts for wiring devices wherein the devices are pushed into mounting openings provided for the purpose, placing mounting arms of spring material under tension, with the mounting arms ultimately springing into abutting engagement with the opposed corners of the mounting opening when the wiring device ultimately is pushed home.
Mounting means of this type are generally incorporated on wiring devices of the so-called OEM ("original equipment manufacturere") type, where they are commonly used as labor-saving and time-saving mounts, enabling quick assembly of switches, receptacles, incandescent lamp sockets and the like with the metal plates of stoves, ovens, refrigerators, etc.
2. Description of the Prior Art
It is well known in the prior art to utilize snap-in mounting springs on wiring devices of the general types described above. Normally the mounting springs are made in a single piece of strip metal material, having suitable spring characteristics. However, it is not unknown to provide mounting springs that are in actuality comprised of separate, opposed spring arms. In either instance, it is conventional practice to first form the piece in a progressive die from, for example, AISI C1050 cold rolled annealed spring steel. Then, the completed piece is hardened and tempered in a final production step that has added considerably to the manufacturing cost.
In either type, the mounting means incorporates a pair of opposed, opposite but identical spring arms which are normally extended in diverging relation, and have free end portions that are inwardly offset and are formed with reentrant angles. In one portion of the reentrant angle formations of the spring arms, transverse series of serrations are provided. When the mounting spring is pressed into the mounting opening, the arms are initially placed under tension, but when the wiring device is pushed home, the arms are freed to spring outwardly, in such fashion that the formed angle and serrations grip the opposed corners of the mounting opening, thereby securely and fixedly retaining the mounting device in its proper, mounted position in the metal plate of the stove, range hood, medicine cabinet, or other appliance in which the wiring device is to be mounted.
In the prior art, difficulties have been experienced in the use of mounting springs of the type described. These difficulties arise, in many instances, due to hydrogen embrittlement.
Also, in the prior art the cost has been increased substantially by the necessity of a separate hardening and tempering process of the pieces after they are formed.
It has been found, in using high-tensile spring steels that are inherently of a temper and strength sufficient to dispense with the conventional hardening step, that there is a great tendency in the snap-in spring forming tools, to break or crack the piece at the location of the serrations. The serrations are formed in the spring metal strips by punches or equivalent inserts provided in the dies. When serrations are formed extending across the full width of the metal strip, such inserts or punches wear rapidly, and the piece parts tend to come out of the die with serrations that are not sharply V-shaped, often representing little more than grooves extending across the spring-metal part. These, obviously, do not have the gripping capacity that is necessary for spring mounts of the type described, and fail to meet customer's specifications. Indeed, in such instances the wiring device may tend to fall out of the mounting opening after a period of time, during normal use of the appliance, and this not only is productive of customer complaints, but even can represent fire hazards or other safety hazards.
One solution to at least part of these problems, relating to the cost of hardening and tempering the completed production parts, is to use a specially constituted steel that does not require the separate hardening step. This has not heretofore been possible due to rupture of the part in the die when such materials are used.